The invisible watermark — AI-written text can now be identified, and what that means for your business

On Tuesday, 11 August, Anthropic confirmed a change this column has been expecting for a while: text generated by its newest Claude models now carries an invisible watermark, woven into the words themselves, everywhere Claude is used, worldwide. Supported files such as images get a signed provenance label on top, under the industry C2PA standard. The trigger is European law — the EU AI Act’s transparency rules became enforceable for newly launched AI systems on 2 August — but rather than run a separate European version, Anthropic is applying the marking globally.

OpenAI, Google, Microsoft, and Meta have signed the same European code of practice, and platforms have begun flagging AI content on their own initiative. The direction is settled: AI-generated content is becoming identifiable. Any business that has built AI into its weekly routine, as this column has been encouraging for ten weeks, should understand what that means before the detection tools land in other people’s hands.

New Claude models watermark their text at the model level, wherever Claude is used — withsigned provenance labels on files beyond text. (Branded graphic by PGH Consulting, LLC) What actually changed Claude models launched on or after 2 August 2026 mark their output from day one; Anthropic says marking for its older models is being worked on during a transition period the law allows. The watermark is applied at the model level, which means it is present whether you use Claude in the browser, through the API, in Claude Code, in the Cowork desktop tool this column covered in Week 5, or through the big cloud platforms.

The mark itself is not a visible stamp. It is a statistical pattern in the choice of words, imperceptible to a reader, that specialised software can test for. Anthropic says it does not change the meaning, quality, or readability of the text.

Because the pattern lives in the text itself, it travels with copy and paste, and it can survive a degree of editing. How much editing removes it, Anthropic has not said. Detection is the part still in progress: the company has committed to helping users and third parties check content for Claude’s marks, with technical documentation promised.

So “everyone can tell” is where this is going rather than where it is this morning — but the text you generate today carries the mark that tomorrow’s tools will rea…